Each musical instrument has its own unique resonance signature. This signature is what makes one type of instrument sound different from another and why two specimens of the same type of instrument do not sound the same. In a piece of music, it is the interplay of these unique resonance signatures that is crucial to conveying the musical idea of a composer, arranger, or performer.
It is a goal of an audio playback system, in particular a “high-end” audio system, to faithfully reproduce this interplay, as recorded on a recording medium (e.g., lp, cd, tape, etc.). To do so, the audio system must extract the recorded musical signal without altering it and convert it to sound.
Challenging an audio system's ability to faithfully reproduce the recorded musical signal—and hence re-create the original musical event—is the system's susceptibility to mechanical resonances and vibrations. To the extent that an audio system has its own resonant signature, as imparted by such vibrations, it functions as an instrument. Such an audio system will color every instrument that it tries to reproduce, taking the listener further from a faithful re-creation of the original musical event.
A typical “high-end” audio system will include one or more source components (e.g., cd-player, turntable, etc.), a preamplifier, an amplifier and speakers. The spectral signature of these components is affected both directly and indirectly by mechanical resonances and vibrations. As to direct effects, these components are subjected to vibrations and resonances due to:                Mechanical coupling. The most significant source of mechanically-coupled vibration is the music itself. High-amplitude, low-frequency sound from the speakers mechanically couples through the floor of the listening room, up through the equipment rack into the bottom of a component. Furthermore, very-low-level, low-frequency vibrations from passing vehicles, machinery and other sources can couple through the floor into audio components.        Acoustic pressure. Air-borne energy generated by the loudspeaker/room interface can directly couple to equipment racks, equipment enclosures, and then to signal-generating components.        Internal vibrations. Vibrations arise from sub-systems within the audio components themselves, such as mechanical drive systems (e.g., in cd players and turntables, etc.), spinning cooling fans (e.g., in amplifiers), and humming transformers. Even electric current moving through wires or other components can be a source of vibration. Specifically, current-induced magnetic fields that form around transformers, wires, and other passive devices can cause these components to vibrate or move slightly within their own fields. This creates minute non-linear currents that can subtly alter the original musical signal.        
As to indirect effects, vibrations, varying in magnitude from very large (e.g., cabinet resonances that can be felt) to miniscule, can negatively affect playback through time- and frequency-domain disturbances.
To ameliorate the problems wrought by vibrations and resonances, various resonance- and vibration-control products have been developed. The products can be grouped generally into two classes: (1) footers and (2) platforms. Reducing vibrations and resonances through the use of these products has, in some cases, resulted in improvements in imaging, tonal balance, timing, treble focus, bass extension and detail.
Footers, as the name implies, are devices that are placed underneath an audio component and that replace the manufacturer-supplied “feet” that are supplied with the component (and which typically function simply as a standoff to prevent contact and damage to an underlying support shelf). A variety of footer designs have been developed, two of which are mentioned below.
In some cases, the footers are formed of a resilient material (e.g., Navcom™ Sorbothane™, etc.) that is intended to damp vibrations before they reach the supported component. In some other cases, the footers are rigid (e.g., cones, spikes, etc.). Although some rigid footers are alleged by their manufacturers to “drain” energy from the supported component, most function by merely shifting the frequency and level of the resonances.
While effective to varying degrees, footers have their drawbacks. In particular, they can be difficult to place under audio components, especially if the components are enclosed in a cabinet. Furthermore, footer-supported components can be somewhat unstable. Resonance/vibration-control platforms address both of these problems.
Resonance/vibration-control platforms include (1) a base or platform on which the isolated component rests and (2) some type of mechanism for providing resonance/vibration-control for the platform. Several resonance/vibration-control platforms in the prior art are surveyed below.
One type of system includes one or more air-filled bladders that are located beneath a plinth (typically formed from medium density fiberboard). As the bladders are inflated, the plinth—and hence the component—“float,” thereby isolating the component from mechanically-coupled vibrations. In a second type of system, a plinth is placed on a substantial volume of sand. The sand conforms to the entire surface of the plinth and efficiently constrains and partially damps the platform's vibrational modes.
In a third type of system, several thermally-reactive copolymers are used as the primary damping material. The copolymers are contained in several modules underneath a plinth. Each different copolymer is intended to control resonances within a certain frequency range. The copolymers possess an ability to rapidly change darometer (i.e., relative hardness or softness). Movement or vibration creates friction in the module, which produces heat. The heat changes the darometer of compound in a pre-calculated manner based on the weight of the component it supports. As vibrations pass through the various modules, their amplitude decreases until they are substantially dissipated.
In a fourth type of system, magnetic levitation is used to isolate a supported component. In this system, coupled magnets that are oriented for repulsion are disposed underneath a plinth.
These various systems have drawbacks. For example, the technology and materials used in some of these systems are expensive, pushing the retail cost of some of these systems upwards of $1000. In some air-based systems, the air leaks out over time, requiring a user to occasionally re-balance the system by adding more air. For some systems, the customer provides information about the weight, weight distribution, and size of a component of interest and then the resonance/vibration-control system is designed based on these parameters. This limits the suitability of the platform for other equipment should the purchaser decide to replace the component for which the platform was designed. Some systems, such as magnetic levitation platforms, are particularly sensitive to uneven loads. In this regard, footers have an advantage since they can be appropriately positioned under a component to address an uneven weight distribution.
Many of the current resonance/vibration-platforms offer little flexibility to adapt to changes in the playback system. And no one resonance/vibration-control system is best for all components (e.g., one manufacturer's turntable vs. another's, etc.) in all situations (e.g., room construction, etc.). This is problematic because many audiophiles change their playback systems on a regular basis (at least compared to the music-listening public at large). Consequently, an “upgrade” in a source component might downgrade a playback system's ability to reproduce a recorded musical signal because a previous choice in a vibration-control platform is not suited to the new source component. This “upgrade” then occasions another purchase—a new vibration/resonance-control platform that is hopefully better suited to the new source component.
Consequently, there is a need for an improved resonance/vibration-control system.